1. Technical Field
The present invention relates to a near-field optical head which can record various kinds of information with extra high density on a magnetic recording medium by a near-field light, and an information recording/reproducing device which includes the near-field optical head.
2. Background Art
Recently, along with the increase of the capacity of a hard disk in a computer device or the like, recording density of information in a single recording surface has increased. For example, to increase the recording capacity per unit area of a magnetic disk, it is necessary to increase the surface recording density. However, along with the increase of the recording density, a recording area which 1 bit occupies on a recording medium has decreased. When the bit size becomes small, energy which information that 1 bit possesses approximates heat energy at a room temperature and hence, there arise drawbacks of thermal demagnetization such as the inversion or the dissipation of recorded information due to thermal fluctuation or the like.
As a longitudinal recording method which is used in general, there has been known a method for recording magnetism where the direction of magnetization is directed in the in-plane direction of a recording medium. In this method, however, the dissipation of the recorded information or the like is liable to occur due to the above-mentioned thermal demagnetization. To overcome such a drawback, the recording method has been replaced by a perpendicular recording method which records a magnetization signal in the direction perpendicular to a recording medium. This method is a method which records magnetism information based on a principle which allows a single magnetic pole to approach a recording medium. According to this method, a recording magnetic field is directed in the direction substantially perpendicular to a recording film. Information recorded by a vertical magnetic field can, since it is difficult for an N pole and an S pole to form a loop in a recording film surface, hold information in a stable manner in terms of energy. Accordingly, the perpendicular recording method exhibits strong resistance against thermal demagnetization in the longitudinal recording method.
However, to satisfy the needs for the recording/reproduction of larger-volume and higher-density information, in the near future, a recording medium will be in demand to satisfy the further increase of recording density. Accordingly, to minimize the influence between neighboring magnetic domains and thermal fluctuation, a recording medium which possesses a strong coercive force has started to be adopted these days. Accordingly, also in the above-mentioned perpendicular recording method, it has been difficult to record information on this recording medium.
To overcome this drawback, there has been proposed a hybrid magnetic recording method (a near-field-light assisted magnetic recording method) which temporarily lowers a coercive force by locally heating a magnetic domain with a near-field light and performs writing during a time that the coercive force is lowered. This hybrid magnetic recording method is a method which makes use of a near-field light caused by an interaction between a minute region and an optical aperture formed in a size not more than a wavelength of light formed by a near-field optical head. In this manner, by making use of the minute optical aperture which exceeds a diffraction limit of light, that is, a near-field optical head which includes a near-field light generating element, it is possible to handle optical information in a region where the size of the optical aperture becomes not more than a wavelength of light which is considered to be a limit in the conventional optical system. Accordingly, it is possible to achieve high densification of recording bits which exceeds a conventional optical information recording/reproducing device or the like.
Here, the near-field light generating element may be, besides the above-mentioned optical minute aperture, constituted of a projecting portion formed in a nanometer size, for example. With the use of such a projecting portion, it is possible to generate a near-field light in the same manner as the optical minute aperture.
As a recording head which adopts the above-mentioned hybrid magnetic recording method, there have been proposed various kinds of recording heads. As one of such recording heads, there has been known a magnetic recording head which aims at the increase of recording density by contracting a size of a light spot (for example, JP-A-2004-158067, JP-A-2005-4901).
The magnetic recording head mainly includes a main magnetic pole, an auxiliary magnetic pole, coil winding where a spiral conductive pattern is formed inside an insulator, a metal scatterer which generates a near-field light from radiated laser beams, a planar laser light source which radiates laser beams toward a metal scatterer, and a lens which condenses the radiated laser beams. These respective constitutional parts are mounted on a distal end surface of a slider which is fixed to a distal end of a beam.
The main magnetic pole has a surface which faces a recording medium on one end side thereof, and has the other end side thereof connected to the auxiliary magnetic pole. That is, the main magnetic pole and the auxiliary magnetic pole constitute a single magnetic-pole-type vertical head which arranges one magnetic pole (single magnetic pole) in the vertical direction. Further, coil winding is fixed to the auxiliary magnetic pole such that a portion of the coil winding passes between the magnetic pole and the auxiliary magnetic pole. These magnetic pole, auxiliary magnetic pole and coil winding constitute an electric magnet as a whole.
The above-mentioned metal scatterer made of gold or the like is mounted on a distal end of the main magnetic pole. Further, the above-mentioned planar laser beam source is arranged at a position spaced apart from the metal scatterer and, at the same time, the above-mentioned lens is arranged between the planar laser beam source and the metal scatterer.
The above-mentioned respective constitutional parts are mounted in the following order: the auxiliary magnetic pole, the coil winding, the main magnetic pole, the metal scatterer, the lens, the planar laser beam source from a distal-end-surface side of the slider.
When using the magnetic recording head having such a construction, a recording magnetic field is applied simultaneously with the generation of the near-field light, thus recording various kinds of information on the recording medium.
That is, laser beams are radiated from the planar laser beam source. The laser beams are converged by a lens, and are radiated to the metal scatterer. Due to such radiation of laser beams to the metal scatterer, free electrons in the metal scatterer are uniformly oscillated due to an electric field formed by the laser beams and hence, plasmons are excited whereby a near-field light is generated in the distal end portion. As a result, the magnetic recording layer of the recording medium is locally heated by the near-field light so that a coercive force is temporarily lowered.
Further, simultaneous with the above-mentioned radiation of laser beams, a drive current is supplied to the conductive pattern of the coil winding so as to locally apply a recording magnetic field to the magnetic recording layer of the recording medium near the main magnetic pole. Accordingly, it is possible to record various kinds of information on the magnetic recording layer whose coercive force is temporarily lowered. That is, recording of various kinds of information on the recording medium is performed due to the cooperative actions of the near-field light and the magnetic field.    Patent document 1: JP-A-2004-158067    Patent document 2: JP-A-2005-4901
The above-mentioned conventional near-field optical head, however, still has following drawbacks.
That is, in generating the near-field light inevitable for recording information, the laser beams are converged and radiated to the metal scatterer from the planar laser beam source by way of the lens. However, since the metal scatterer is mounted on the distal end of the main magnetic pole, laser beams must be radiated with an optical axis of laser beams from the planar laser beam source arranged in oblique posture. Accordingly, even when the positional adjustment of the lens position is carried out favorably, it is difficult to efficiently condense laser beams on the metal scatterer. Particularly, since it is necessary to arrange the lens while taking the interference with the recording medium into consideration, a semicircular lens is used. The use of such a lens also causes lowering of condensing efficiency.
As a result, the near-field light cannot be generated efficiently and hence, there may be a case where writing of information is not possible.
Further, it is necessary to arrange the lens at a position spaced-apart from the metal scatterer and hence, a size of the head becomes large whereby the head cannot have the compact constitution. Still further, it is necessary to arrange the planar laser beam source while taking the position of the lens and the position of the metal scatterer into consideration and hence, the head cannot be easily installed.